Semiconductor laser elements for DVD-Rs, CD-Rs, Blu-Ray disks and the like are required to have high output power. In a semiconductor laser device, such a semiconductor laser element is mounted either directly or via a submount on a highly efficient heat sink to dissipate heat generated from the semiconductor laser element. The heat sink is fixed to a top surface of a disk-shaped base in such a way that an element mount surface is perpendicular thereto. The base has, in the top surface thereof, a depression that is located immediately below the semiconductor laser element. As disclosed in Patent Publication 1, this depression is mainly used for receiving a monitoring light-receiving element to be disposed therein or a lead pin to be disposed therein that receives a signal from a light-receiving element that also serves as a submount.
A high output power semiconductor laser element can be achieved by making longer the cavity length of the semiconductor laser element. Thus, we have made higher the heat sink to make longer the semiconductor laser element, only to find that the position of the luminous point of the semiconductor laser element varies. The problem here is that such an element does not conform to standard specifications, and makes the device larger. We have also made the base thinner, only to find that the thinner base reduces the heat capacity, leading to reduced heat dissipation characteristic.
Therefore, Patent Publication 2 discloses a semiconductor laser device that permits the mounting of a longer semiconductor laser element without changing the position of the luminous point of the semiconductor laser element by disposing the semiconductor laser element in such a way that part thereof projects into a depression formed in a top surface of a base.
However, when a heat sink is formed separately from the base, an error, if any, that occurs when the heat sink is mounted thereon makes an element mount surface not flush with an inner side surface of the depression. When the element mount surface is located outside the rim of the depression, a lower end portion of the semiconductor laser element or the submount makes contact with the inner side surface of the depression with priority, forming clearance between it and the heat sink. The clearance thus formed narrows the heat dissipation path, and thereby impairing the heat dissipation characteristic. Moreover, even when the heat sink portion and the base portion are formed in one piece, an upper part of the element mount surface located above the base becomes more recessed than a lower part thereof after post-processing of the element mount surface such as metal stamping and polishing, producing surface discontinuity. In this case, the semiconductor laser element or the submount does not make close contact with the heat sink, as in the case where they are formed separately, impairing the heat dissipation characteristic.    Patent Publication 1: Japanese Patent Application Laid-Open No. 2001-267674    Patent Publication 2: Japanese Patent Application Laid-Open No. 2004-179494